SYDNEY, Dec. 12 (Xinhua) -- Animals that stop reproducing, whether through hormonal contraception or surgical sterilization, live 10 to 20 percent longer on average, researchers have found.
Drawing on data from the records of 117 captive mammal species, from lions to rats, an international team of researchers examined the trade-off between living a long life and having babies, a media release from Australia's University of New South Wales (UNSW) said Friday.
"These findings offer some of the strongest evidence yet for one of evolutionary biology's central ideas, reproduction shortens lifespans," said UNSW biologist Malgorzata Lagisz, co-author of the study published in Nature.
Evolutionary theory holds that the energy devoted to producing and raising offspring comes at the expense of repairing cells and maintaining long-term health, researchers said.
Comprehensive zoo records, linking birth, death, and reproductive management through contraception or sterilization, have allowed researchers to compare longevity across a wide range of mammal species, according to the study led by New Zealand and Australian researchers.
The study found differing mechanisms between sexes. In males, only castration extends lifespan, particularly when conducted pre-puberty, likely by reducing testosterone-driven risky, aggressive behaviors that often lead to injury or early death.
"The biggest longevity boosts occurred when males were castrated early in life," said Lagisz.
In females, both contraception and surgical sterilization consistently extended female lifespans across species regardless of timing, the study showed.
"Pregnancy, lactation and repeated reproductive cycles are not only metabolically taxing but can weaken the immune system," Lagisz said, adding freed from reproductive demands, females retain more resources to fuel their immunity and tissue repair, reducing their risk of infection.
The findings also help explain the evolution of menopause, as it may offer later-life survival benefits.
The researchers caution against applying the findings directly to human health decisions, noting that "access to health care, medicine, nutrition and social support dramatically buffers the physical hardships of reproduction." ■
